The present invention relates to a gas injection molding apparatus and method, and more particularly, to a resin injection molding apparatus and method in which gas injected into a first-formed product is exhausted to add a different resin in gas injection molding.
In general, the injection molding is one of the plastic molding methods. A gas injection molding technique was invented in the United Kingdom. This gas injection molding involves a molding technique where gas is injected simultaneously when resin is put into a mold to form the shape of the resin in a hollow, reducing the material and the molding pressure of an injection molding apparatus.
A conventional injection molding apparatus, as shown in FIG. 1, comprises a mold 1 for manufacturing a resin product 3, an injection path 4 for providing resin and gas into a hollow 2 formed inside mold 1, an injector 5 for compressing the resin to injection path 4, and a gas supply 6 for feeding gas to injection path 4.
Injector 5 includes a nozzle 7 on the border of injection path 4. Gas supply 6 has a gas intake 8 on the border of injection path 4.
The operation of the conventional gas injection molding apparatus will be discussed below.
As resin is filled in injection path 4 and product 3 through nozzle 7 by 70-80% of the volume of the product, nozzle 7 of injector 5 is closed. Gas then comes into injection path 4 via gas intake 8.
The gas enters the center portion of product 3. The resin filled in hollow 2 is dispersed uniformly in hollow 2 under the pressure of the gas. The center portion of hollow 2 is continuously filled with the gas.
The cross section of the product formed by the conventional gas injection molding is shown in FIG. 2.
In the conventional gas injection molding apparatus, however, there sometimes occurs a case in which the gas is exposed on the surface of the hollow, deteriorating the exterior of the product.
In addition, the conventional gas injection molding apparatus is not capable of re-enforcing the stiffness of resin good in roughness but fragile in stiffness.